Implantable Cardioverter Defibrillator (ICD) After Cardiac Arrest

An implantable cardioverter defibrillator (ICD) is a small, battery-powered medical device that continuously monitors your heart rhythm and delivers a life-saving electric shock if it detects a dangerous arrhythmia. For cardiac arrest survivors, an ICD is the most common long-term protective treatment — effectively a defibrillator living inside the chest, ready to act within seconds if the heart goes into ventricular tachycardia or ventricular fibrillation again.

What Is an Implantable Cardioverter Defibrillator?

The device is smaller than a mobile phone and sits under the skin just below the collarbone, usually on the left side of the chest. It has two main parts: a pulse generator (a sealed titanium case containing the battery and a small computer) and one or more leads (thin insulated wires that run from the generator into the heart via a vein). The pulse generator monitors every heartbeat, and the leads both sense the heart’s electrical activity and deliver therapy when needed.

Guidance and information about the device are also available from the British Heart Foundation and the NHS, both of which are useful alongside this page.

When Is an Implantable Cardioverter Defibrillator Recommended?

An ICD is recommended for people who are at high risk of a life-threatening ventricular arrhythmia — primarily ventricular tachycardia (VT) or ventricular fibrillation (VF). These are the two rhythms most commonly responsible for sudden cardiac arrest. Broadly, there are two reasons a cardiologist might recommend an ICD:

Secondary prevention — you have already had a cardiac arrest, sustained VT, or VF that was not caused by a reversible factor. Most SCA UK survivors fall into this category.
Primary prevention — you have a condition that significantly raises your risk of sudden cardiac arrest (for example, cardiomyopathy with reduced ejection fraction, a channelopathy such as long QT syndrome or Brugada syndrome, or a strong family history of sudden cardiac death), but you have not yet had an event.

The decision to implant is made by an electrophysiologist (a cardiologist specialising in heart rhythm disorders) after detailed assessment. For more on the underlying rhythm problems, see our page on Arrhythmia.

Types of Implantable Cardioverter Defibrillator

Not all devices are the same. The main types of implantable cardioverter defibrillator in use today are:

Single-chamber ICD — one lead placed in the right ventricle. The most common configuration for straightforward secondary prevention.
Dual-chamber ICD — one lead in the right atrium and one in the right ventricle. Used when pacing support is also needed.
CRT-D (cardiac resynchronisation therapy defibrillator) — three leads, used for people with heart failure where the two ventricles need to be coordinated.
Subcutaneous ICD (S-ICD) — a newer design where the entire system sits under the skin, with no leads inside the heart or blood vessels. Useful for younger patients, those with vascular access issues, or those at higher risk of lead infection.
Extravascular ICD (EV-ICD) — the newest category, where the lead sits behind the breastbone rather than inside the heart. Still relatively uncommon in the UK but increasingly available.

How an ICD Is Implanted

Implantation is usually carried out under local anaesthetic with sedation, though general anaesthetic may be used for an S-ICD or more complex devices. A small incision is made just below the collarbone, and a pocket is created for the pulse generator either under the skin or under a muscle. The leads are then passed through a vein and positioned in the heart under X-ray guidance. Once in place, the device is programmed and tested before the incision is closed.

The procedure typically takes one to two hours, and most people go home either the same day or the next morning. Full healing of the pocket takes several weeks, and there are specific precautions to follow during that recovery period — see our page on ICD Protection After Surgery for detailed guidance.

How an Implantable Cardioverter Defibrillator Works

The ICD monitors every heartbeat continuously. If it detects a rhythm that falls within its pre-programmed treatment zones, it delivers therapy automatically. Your cardiologist programmes the device with the settings most appropriate for your condition. Depending on what the device sees, it can deliver one or more of the following:

Anti-tachycardia pacing (ATP) — for some types of ventricular tachycardia, the ICD delivers a rapid sequence of small pacing pulses to interrupt the fast rhythm. You usually feel nothing.
Cardioversion — a mild synchronised shock to restore normal rhythm. You may feel this as a thump in the chest.
Defibrillation — a strong shock to stop ventricular fibrillation and restart a normal rhythm. This is the life-saving therapy most people associate with an ICD.
Bradycardia pacing — if the heart beats too slowly, the device can pace it at a safe rate, much like a standard pacemaker.

What an ICD Shock Feels Like

Pacing and ATP are usually not felt at all. A cardioversion may feel like a hard thump in the chest. A full defibrillation shock is more intense — survivors commonly describe it as being kicked in the chest or feeling like a sudden electric jolt. It is over in a fraction of a second. Many people find the emotional impact of a shock harder than the physical sensation, particularly if it was unexpected. Knowing what to do before, during, and after a shock can make a real difference to recovery.

For detailed guidance see our pages on ICD Shocks: What You Need to Know and How to Respond to an ICD Shock.

Living With an Implantable Cardioverter Defibrillator

An ICD manages arrhythmia; it does not cure the underlying heart condition. In most cases you will continue to take prescribed medication alongside it, and the device will be checked periodically either in clinic or via remote monitoring. Battery life is typically five to ten years depending on how much therapy the device has delivered, after which the generator is replaced in a short outpatient procedure (the leads usually stay in place).

Key practical considerations for living with an implantable cardioverter defibrillator include:

Driving — DVLA rules require a period off driving after implantation. See Driving and the DVLA for full details.
Electromagnetic interference — modern ICDs are well shielded, but a few environments and devices still warrant caution. See our Precautions and Electromagnetic Compatibility pages.
Airport security and travel — always carry your ICD identification card. Walk through body scanners at normal pace, and inform security if you are asked to use a hand-held wand.
ICD sounds and alerts — some devices beep or vibrate to indicate issues. Learn what yours does at ICD Sounds and Alerts.
MRI scans — most modern ICDs are MRI-conditional, meaning scans can be performed with appropriate precautions. Always inform the scanning team.
Emotional wellbeing — many people experience anxiety, low mood, or shock-related worry after implantation. This is common and well recognised; counselling and peer support can both help.

Questions to Ask Your Cardiologist

Which type of ICD have I been given, and why was it chosen for me?
What settings is my device programmed to — at what heart rate will it deliver therapy?
When will I be able to drive again, and what DVLA rules apply to me?
How do I care for the wound after surgery?
Is my device MRI-conditional?
Will I feel a shock coming, and what should I do if I receive one?
How and how often will my device be monitored?
What should my partner or family do if they witness me being shocked?